The present invention relates to an ultrasonic motor with high accuracy and a simple structure and a surveying instrument including the ultrasonic motor.
A surveying instrument, e.g., a total station has a telescope unit for sighting a measuring point. The telescope unit is supported by a frame unit rotatably in a vertical direction, and further, the frame unit is supported rotatably in a horizontal direction by a base unit. Further, the total station includes a motor for rotating the telescope unit and a motor for rotating the frame unit.
Further, use of an ultrasonic motor as a motor has been proposed recently. The ultrasonic motor does not require a speed reducer or the like but is directly connected to a rotation shaft (driven shaft) of an object to be driven. Therefore, the ultrasonic motor has merits that an object to be driven can be directly driven, there is no error caused by a backlash or the like, and further, a structure of a driving unit can be simplified.
On the other hand, in an instrument requiring high accuracy as in the surveying instrument, in a case where a driven shaft and an ultrasonic motor are directly connected to each other, a run out of the ultrasonic motor itself or an eccentricity caused by an assembling error when the driven shaft and the ultrasonic motor are directly connected to each other gives an influence on a rotation of the driven shaft. Therefore, there is a fear that a rotational accuracy of the driven shaft deteriorates and in turn a deterioration of a measurement accuracy is incurred.